You will get an error message if you try to import a city that is medium or bigger. The Sims 2 only accepts the small city size. Cities are saved in the “MyDocs\SimCity4\regions\ name of region” folder as name of city.SC4. When you add a region, select the plain option, the ocean is not very useful because it's harder to see your brush underwater.
So it is easier to make a region for your Sims 2 creations.
